1. Field of the Invention
The present invention relates to a polyester fiber of improved dyeability and to a process for the preparation thereof. More particularly, the present invention relates to a polyester fiber which can be dyed deep color under normal pressure and boiling conditions. That is, the present invention relates to an modified polyethylene terephthalate fiber which is easily dyeable while retaining the excellent properties inherent to polyethylene terephthalate, and a process for the preparation thereof.
2. Description of the Prior Art
Polyester fibers, particularly those consisting mainly of polyethylene terephthalate (hereinafter referred to as PET fiber), have a high degree of crystallinity and a high softening point, and thus, are excellent in mechanical properties, such as strength and elongation, thermal resistance and chemical resistance. Therefore, the PET fibers are widely used in the fields of industrial materials and garments.
On the other hand, the PET fibers have, in addition to the above-mentioned advantages, the disadvantages that deep color dyeing is difficult, pilling is likely to occur, static electricity is likely to generate and the hygroscopicity is low. Furthermore, because the PET fibers have various disadvantages concerning dyeing, especially they are difficult to be dyed deep color, the range of their use is limited.
In general, the PET fibers are dyed with a disperse dye because they contain a hydrophobic group in their molecular structure. Because the PET fibers are highly crystalline, and has a dense structure, they are dyed by either (1) high-temperature and high-pressure dyeing at a temperature of 120.degree. C. to 130.degree. C. or (2) carrier dyeing which is carried out at a temperature of about 110.degree. C. or under normal pressure and boiling conditions. The high-temperature and high-pressure dyeing (1) has, however, the disadvantages that the operation of the machine or apparatus used for dyeing is complicated and the energy cost is high. Furthermore, when the PET fibers are dyed in the same dyeing bath in combination with other fibers, especially acrylic fibers, wool or the like, by the high-temperature and high-pressure dyeing method, the physical properties of the other fibers are deteriorated, for example, the resiliency is reduced. Therefore, it is substantially difficult to utilize this method. On the other hand, the carrier dyeing (2) has disadvantages in that the carrier as a dyeing auxiliary agent is difficult to handle, and treatment of the waste liquor is difficult, because the carrier generally is a harmful material. Furthermore, because the carrier occupies a dye-depositing site in the fiber, deep color dyeing is difficult or the migration of the dye is likely to occur. These phenomena may result in an unevenness in dyeing.
Therefore, a variety of methods have been proposed for overcoming the above-mentioned disadvantages of the PET fibers. One typical method is to introduce a copolymerizable component into a PET polymer.
For example, Japanese Examined Patent Publication (Kokoku) No. 34-10497 discloses (a) a method in which a compound containing a metal sulfonate group is copolymerized with polyethylene terephthalate. Japanese Examined Patent Publication (Kokoku) No. 54-38159 proposes (b) a method in which a compound containing an amino group is copolymerized with polyethylene terephthalate. These methods (a) and (b) are characterized by enabling the PET fibers to be easily dyed with a basic dye and an acid dye as well as disperse dye. Also, as a copolymerizable component used for enhancing only the dyeability of the PET fibers with a disperse dye, there are well known (c) dicarboxylic acids, for example, isophthalic acid and adipic acid, and polyalkylene glycols, for example, polyethylene glycol.
These methods all have disadvantages, however, for example, the method (a) is disadvantageous in that a metal sulfonate group-containing compound as the raw material is expensive, and further, polymerization and spinning cannot stably be carried out. A PET fiber containing an amino group-containing compound in a copolymerized form is disadvantageous in that the polymer has a poor thermal stability. Furthermore, in order to dye the PET fiber deep color to a satisfactory degree under normal pressure and boiling conditions without the use of any carrier, either of these methods (a) and (b) require that a large amount of the copolymerizable component should be copolymerized with polyethylene terephthalate as in the method (c). The use of a large amount of the copolymerizable component results in an extreme reduction in the excellent properties inherent to the PET fiber. In addition, if polyethylene glycol or the like is used as the copolymerizable component, another disadvantages, such as foaming during polymerization and discoloration of the polymer, arise.
As another method for enhancing the dyeability of the PET fiber, there is known a method using high speed spinning, as disclosed in Japanese Unexamined Patent Publication (Kokai) No. 55-107511, and U.S. Pat. Nos. 4,156,071, 4,134,882 and 4,195,051. However, this method is still unsatisfactory in dyeing the PET fiber deep color under normal pressure and boiling conditions without using a carrier. Furthermore, this method has the disadvantage that the shrinkage in boiling water is remarkably reduced as the take-up speed is increased.
It is also known to enhance the dyeability of the PET fiber by subjecting a polyester with which a metal sulfonate compound is copolymerized to high speed spinning (Japanese Unexamined Patent Publication (Kokai) No. 53-139820). Indeed, this method is effective for enhancing the dyeability, and is able to provide a fairly deep color under normal pressure and boiling conditions without the use of any carrier. However, as described hereinabove, the disadvantages of the polymer itself are still present. Furthermore, this method is unable to solve the problem of the reduction of the shrinkage in boiling water due to the high speed spinning.
In addition, Japanese Unexamined Patent Publication (Kokai) No. 57-161121 discloses a method for enhancing the dyeability of PET fibers in which PET fibers obtained by high speed spinning is heat treated. In this case, the PET fibers consist essentially of ethylene terephthalate homopolymer, and the dyeability of such fibers can be enhanced. However, the high speed spinning and the heat treatment cause the resultant fiber to exhibit a further reduced shrinkage in boiling water.
Generally, when a polyester is subjected to high speed spinning, the dyeability of the resultant fiber is improved to some degree, while a reduction in the shrinkage in boiling water due to the increase in the winding speed is outstanding. In the past, especially a winding speed of not less than 6,000 m/min inevitably reduced the shrinkage in boiling water to 4% or less. In order to enhance the dyeability by high speed spinning, while keeping a good balance of the strength and the elongation, the spinning operation should be carried out at a winding speed of not less than 5,000 m/min, preferably not less than 6,000 m/min. As an attempt to further enhance the dyeability, conventional copolymerized PET polymers were subjected to high speed spinning. However, this attempt was still unsatisfactory in improving the reduction in the shrinkage in boiling water.
Table 1 indicates the results of dyeability and shrinkage in boiling water measured for various copolyester fibers obtained by the high speed spinning thereof. It is apparent from the table that the reduction in the shrinkage in boiling water due to high speed spinning cannot be improved merely by subjecting the copolymerized polyesters to high speed spinning.
TABLE 1 __________________________________________________________________________ Degree of Shrinkage in Copolymerized Copolymerization Spinning speed exhaustion boiling water component ratio (Km/min) 100.degree. C. .times. 60 min (%) __________________________________________________________________________ 1 Isophthalic acid 5 mole % 8 83.5 3.5 2 Isophthalic acid 10 mole % 8 86.2 3.8 3 Isophthalic acid 15 mole % 6 82.3 5.0 4 Isophthalic acid 15 mole % 8 90.3 4.5 5 Polyethylene glycol 11 wt. % 8 92.1 4.0 6 Isophthalic acid/ 5 mole % 8 88.2 4.7 polyethylene glycol /3 wt. % 7 5-sodium sulfoiso- 2.3 mole % 8 90.7 4.8 phthalic acid 8 Bisphenol A 5 mole % 6 84.4 5.0 __________________________________________________________________________